1. Field of the Invention
The present invention relates to a styrene copolymer with syndiotactic regularity, more particularly, to a graft copolymer of a syndiotactic polystyrene prepared from styrene and a macromonomer, and a method for the preparation thereof.
2. Description of the Related Art
Polystyrene is generally prepared by radical polymerization in a tactic stereo regularity and has a good processability for extrusion or injection molding and other excellent physical properties, making it widely utilizable for industrial and household applications. However it, as a thermoplastic material, has shortcomings of weakness in heat resistance, impact resistance and chemical resistance.
The syndiotactic polystyrene prepared by metallocene catalyst is a crystalline polymer with high degree of stereo regularity and has enhanced heat resistance and chemical resistance as well as excellent electrical property. (Macromolecules, 1986, 19, 2464).
But it still has the same shortcomings in impact property as atactic polystyrene. For variety of application, improvement in the properties such as impact resistance and compatibility with other polymer materials is required.
Several remedies have been introduced in order to improve impact resistance or impart elasticity to the syndiotactic polystyrene. U.S. Pat. No. 5,247,020, presents the method of blending syndiotactic polystyrene with elastomer during the polymerization process. The method suggests syndiotactic polymerization of styrene in the presence of elastomers such as styrene-butadiene block copolymer, or styrene-isoprene block copolymer.
Also, in order to solve the problem, presented are the methods of random or block copolymerization with other monomers. In U.S. Pat. No. 5,475,061 and U.S. Pat. No. 5,554,695, syndiotactic copolymerization with acryl monomer is presented. U.S. Pat. No. 5,260,394 describes random copolymer of syndiotactic polystyrene obtained by copolymerization with olefins such as ethylene and propylene or conjugated dienes such as butadiene and isoprene. The syndiotactic copolymers obtained by these methods have low glass transition temperatures, exhibiting enhanced processability and elasticity. U.S. Pat. No. 6,271,313 presents the syndiotactic polystyrene block copolymer prepared from styrene and butadiene monomer. But the activity of catalyst of the polymerization decreased in the presence of butadiene and both of low yield and low content of polybutadiene was resulted.
Another alternative method to enhance the impact resistance of the syndiotactic polystyrene, described copolymers obtained from graft polymerization. In U.S. Pat. No. 5,250,629, polyacrylate grafted copolymer is presented, which is prepared by anionic initiation of a syndiotactic copolymer obtained from styrene and p-methylstyrene and subsequent polymerization. Styrene is polymerized in the presence of divinylbenzene and unreacted double bond of divinlybenzene unit in the resulted polymer is used for copolymerization with ethylene to make graft copolymer.
U.S. Pat. No. 5,362,814 introduces a method including copolymerization of diolefins such as vinylnorbornene and divinylbenzene with alpha olefins. The resulted copolymer has unreacted double bond which can be used for copolymerization with styrene. The obtained graft copolymer can be added as compatibilizing agent to a mixture of syndiotactic polystyrene and ethylene-propylene copolymer to give better mixing efficiency
U.S. Pat. No. 6,025,447, presents the graft copolymer which is prepared by copolymerization of styrene and a copolymer of diene and styrene with styrenyl group attached to main chain. However, the modification of the copolymer of styrene and butadiene to introduce styrenyl group requires multiple chemical steps such as hydrofomylation of vinyl group of polydiene moiety and subsequent coupling reaction with vinylaomatic unit.
In EU Pat. 1,077,224, copolymers obtained from a macromonomer of polybutadiene or polyisoprene and styrene or its derivatives are suggested. The macromonomer was prepared by anionic polymerization of styrene, butadiene, isoprene or vinypyridine and terminal modification of living polymer anion. In EU Pat. 1,118,639, the polymer compositions made of this copolymer was shown to have an enhanced impact resistance. These prior arts using macromonomers require complex chemical steps in the preparation of macromonomer. The preparation methods generally need low temperature to prevent the formation of the by-products, (Macromol. Rapid commun. 1998, 19, 563) or requires excessive usage of terminal modifier, (Polymer Bulletin 1990, 24, 1) giving problems in separation and purification of the macromonomer.
The present invention provides a styrene copolymer in which polymeric chains capable to implement elasticity and impact resistance are attached to syndiotactic polystyrene and the preparation method thereof.
Styrene copolymer of the present invention is prepared by the steps of:
a. preparing living polymer with anion activity by polymerizing anionically polymerizable monomer in the presence of alkyllithium catalyst in a non polar solvent;
b. making macromonomer by reacting terminal modifier having a structure represented by the formula 1 with the above living polymer; and
c. copolymerizing the abovementioned macromonomer and styrene monomer in the presence of transition metal catalyst and co-catalyst. 
wherein, Y is Si or Sn atom, R is individually same or different C1-20 alkyl group or aryl group, X is independently same or different Cl or Br, m is an integer and m+n=3.
Another object of the present invention is to provide a grafted copolymer of syndiotactic polystyrene prepared by copolymerization of styrene and macromonomer which is prepared at the ambient temperature with minimized formation of side product and the preparation method thereof.